/*

 * Licensed to the Apache Software Foundation (ASF) under one

 * or more contributor license agreements.  See the NOTICE file

 * distributed with this work for additional information

 * regarding copyright ownership.  The ASF licenses this file

 * to you under the Apache License, Version 2.0 (the

 * "License"); you may not use this file except in compliance

 * with the License.  You may obtain a copy of the License at

 *

 *     http://www.apache.org/licenses/LICENSE-2.0

 *

 * Unless required by applicable law or agreed to in writing, software

 * distributed under the License is distributed on an "AS IS" BASIS,

 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

 * See the License for the specific language governing permissions and

 * limitations under the License.

 */

package com.bff.gaia.unified.runners.fnexecution.control;



import javax.annotation.concurrent.ThreadSafe;

import java.time.Duration;

import java.util.concurrent.TimeoutException;



/**

 * A pool of control clients that brokers incoming SDK harness connections (in the form of {@link

 * InstructionRequestHandler InstructionRequestHandlers}.

 *

 * <p>Incoming instruction handlers usually come from the control plane gRPC service. Typical use:

 *

 * <pre>

 *   // Within owner of the pool, who may or may not own the control plane server as well

 *   ControlClientPool pool = ...

 *   FnApiControlClientPoolService service =

 *       FnApiControlClientPoolService.offeringClientsToSink(pool.getSink(), headerAccessor)

 *   // Incoming gRPC control connections will now be added to the client pool.

 *

 *   // Within code that interacts with the instruction handler. The get call blocks until an

 *   // incoming client is available:

 *   ControlClientSource clientSource = ... InstructionRequestHandler

 *   instructionHandler = clientSource.get("worker-id");

 * </pre>

 *

 * <p>All {@link ControlClientPool} implementations must be thread-safe.

 */

@ThreadSafe

public interface ControlClientPool {



  /** Sink for control clients. */

  Sink getSink();



  /** Source of control clients. */

  Source getSource();



  /** A sink for {@link InstructionRequestHandler InstructionRequestHandlers} keyed by worker id. */

  @FunctionalInterface

  interface Sink {



    /**

     * Puts an {@link InstructionRequestHandler} into a client pool. Worker ids must be unique per

     * pool.

     */

    void put(String workerId, InstructionRequestHandler instructionHandler) throws Exception;

  }



  /** A source of {@link InstructionRequestHandler InstructionRequestHandlers}. */

  @FunctionalInterface

  interface Source {



    /**

     * Retrieves the {@link InstructionRequestHandler} for the given worker id, blocking until

     * available or the request times out. Worker ids must be unique per pool. A given worker id

     * must not be requested multiple times. Note that if the given worker id is never entered into

     * the pool, this call will never return.

     *

     * @throws TimeoutException if the request times out

     * @throws InterruptedException if interrupted while waiting

     */

    InstructionRequestHandler take(String workerId, Duration timeout) throws Exception;

  }

}